Carbon Fiber

Carbon Fibre, also known as graphite fibre, is a highly-developed material that is extremely hard as well as lightweight.1 Carbon fibres are thin strands of carbon, structured in such way that it serves its useful properties. These days, Carbon Fibre is chemically combined with other substances to be applied in areas such as engineering, military and motor sports.2

Timeline

Origins

The first effective use of carbon fibre dates back to the late 1800s, when Thomas Edison, the father of electricity, invented a thin strand of carbons using the hard material of bamboo. The carbonized bamboo which had a very high conductivity, were used as filaments for the earliest light bulbs.3

Development

Although the effectiveness of carbon fibre was long forgotten since, it was brought back in the 1950s when Rayon, a silk-like substance, was used to manufacture it; giving it a very high tensile strength. In the early 1960s, the technology was further developed so that the substance was extremely light but stiff and heat resistant. Ultimately, Rayon was replaced by a similar polymer called PAN (polyacrylonitrile) and such properties gave carbon fibre a vital role in the production of vehicles as they were used in F1 cars and spacecrafts.

Throughout the 1970s and 80s, due to the Cold War, carbon fibre was mainly used in the Department of Defense and Weaponry. Following from the collapse of the Soviet Union, however, the needs of carbon fibre decreased to a dramatic amount and until the 21st Century, it was seldom used.4

Nowadays, carbon fibre can be seen everywhere. It is applied in various of areas including: fashion, sporting goods, industrial, aerospace, energy, and wind energy industries. The high demands for this substance has almost doubled, making it one of the most useful substances around the world. In the future, scientists, specializing in nanotechnology, hope to justify on the substance called Carbon Nanotubes which is very similar to carbon fibre. Improvements in oil exploration and wind energy are also currently investigated in relation to the effective properties of carbon fibre.5

Manufacturing

PAN

In order to produce carbon fibre, the "spinning" process is undergone to create a polymer called polyacrylonitrile (PAN); a vital ingredient for manufacturing carbon fibre. This chemical sequence causes an ammonoxidation reaction between propene and ammonia, as listed below.

Such chemical reaction produces a powdery plastic; Acrylonitrile. This is then polymerised (a method of arranging the structure of the atoms within a particle) to result in a substance of polyacrylonitrile, where the carbon atoms form a long chain polymer. To the right is a diagram showing the structure of the substance.6

Oxidisation

After PAN is produced, the polymer undergoes oxidisation, a process in which forms the basic hexagonal structure of carbon fibre. During oxidisation, PAN is heated at approximately 200-300 degrees so that oxygen is replaced with the hydrogen atoms. This also causes the nitrogen atoms to bond with the corresponding carbon atoms and hence, form repetitive cycles like a crystal.7

Carbonisation

Carbonisation is the process in which the product formed from oxidisation, is heated to an extreme extent (around 1500 to 2000 degrees) so that the elements such as nitrogen, oxygen and hydrogen are removed and thus, leaving a hexagonal structure of pure carbon atoms. The diagram below shows the mechanical change that occurrs due to the addition of heat.89

The carbon fibres, then, are woven into sheets or tubes in a fixed position by an epoxy resin for more effective use.

Environmental Impacts

Positive

When used in vehicles, carbon fibre results in the reduction of toxic chemicals being released into the atmosphere. This is mainly because of its properties of lightening the vehicle and saving at least half of its initial weight. This causes the use of petrol to decline to 30% across the board, making it an environmentally friendly substance.10

Negative

The negative impact of carbon fibre upon the environment can be divided into two parts; manufacturing and post-manufacturing.

Manufacturing - Humongous amount of pollutants are released during the manufacturing of carbon fibre. As explained above, heat is one of the most important ingredients (up to around 1500 degrees celsius) in producing a strand of carbon fibre. Although most of the heating is performed through electrical heating system, this still means that enormous quantity of CO2 and other pollutants are released into the environment. Nitrogen Gas is also emitted into the atmosphere as the polymers (PAN) are burnt off.11

Post-Manufacturing - Since carbon fibre is required all over the world, after its production, more noxious waste is emanated due to its packaging and shipping. The petrol needed for shipping can also disturb the natural sea-life as the pollutants can leak into the water. In addition to this, chemists discovered that carbon fiber can be a threat to human's health. They investigated that carbon fiber dust, which can derive from carbon fibre can cause dust inhalation and skin irritation.12

Chemical Composition

Carbon

Due to its ability to form in different shapes and chains, carbon is undoubtedly, one of the most important elements on the planet. Its allotropes form the basis of organic chemistry and their different structures provide variety of properties, very useful to human beings.

Carbon Fibre

As shown above, carbon fibre is made up of pure carbon and is one of its many allotropes. The chemical composition of carbon fibre includes a sheet of carbon atoms structured in such way that one bonds with two other in a hexagonal shape; similar to a metal lattice except with a single sheet of carbon atom. This gives carbon fibre, its extreme hardness and very light weight.13

Macroscopic Properties and its uses

Properties

Definition

Functions

Ductility

The ability of an object to be stretched into a long wire or hammered into a thin shape. A measure of withstanding tensile stress.

Carbon Fibres are very ductile as it must be stretched into long shapes in order to be applied in different applications. Carbon fibre in clothes, especially, must be in long strands so that it can be woven easily.

Hardness

The ability of a material to resist denting and scratching.

Carbon Fibres are very hard (noticeably harder than steel and other alloys of metals) as some materials have to maintain their shape under great amount of force. In the Defense Department, for example, armoury such as tanks must be extremely hard.

Weight

A measure of mass of an object and the gravitational force upon it.

Carbon Fibers are very light and this is a vital factor for the structure of vehicles as making them lighter means it can move faster with using less force (and hence, less petrol).

Chemical Resistance

The ability to resist chemical reactions with other substances.

When exposed to highly reactive chemicals, carbon fiber is very resistible in undergoing a chemical reaction. This means that applications are highly unlikely to corrode and breakdown due to toxic chemicals.

Electrical Conductivity

The ability to conduct electricity and transfer it through the matter with ease.

The electrical conductivity of carbon fiber in the mechanics of aircraft is very useful as signals can be transferred with ease.

Thermal Expansion

The increase in the dimensions or volume of a substance due to the addition of heat and an increase in temperature.

Low thermal expansion makes carbon fiber suitable for applications where small movements can be critical. Such include telescopes and other optical machinery.

Durability

The ability of an object to last for a durable length of time.

Carbon Fiber and it's high durability makes the material a vital ingredient for applications such as bicycles and shoes which must not easily be worn down.